The present invention relates to apparatus for testing and calibration of flow meters and the like and more particularly to apparatus for measuring flow rate and employing novel tape driven precision encoder means for providing highly accurate flow rate measurements.
Flow meters are utilized in a wide variety of applications which require constant monitoring of the flow rate of a material, such as, liquids and gases. Many flow meters are used in critical applications wherein it is important to both monitor and regulate extremely small flow rates, especially those employed in life sustaining medical applications. It is thus important to test and calibrate flow meters through instrumentation which must necessarily be itself highly accurate in order to accurately test and calibrate the flow meter.
Apparatus which has been designed for flow meter testing and calibration is described in U.S. Pat. No. 3,125,879 issued Mar. 24, 1964 and is comprised of a piston member slidably mounted within a hollow container which receives the flow passing the flow meter under test, said flow filling the container and causing the piston to rise. Means are provided for detecting the movement of the piston past a starting point and a termination point whereby a timer is respectively energized and turned off at the aforesaid starting and termination points. The prior knowledge of the volume of the container together with the elapsed time required for the piston to move between the two aforesaid points yields a flow rate. Suitable sealing means for providing a gas-tight sliding seal between the piston and the container is taught by U.S. Pat. No. 2,927,829 issued Mar. 8, 1960 and comprised of a liquid mercury seal arranged within an annular groove provided in the piston and making wiping contact with the interior of the container.
The apparatus taught in the aforesaid U.S. Pat. No. 3,125,879 has a number of drawbacks among which are the complications in the use of the equipment and the inaccuracies in the readings developed by the equipment due to inherent shortcomings in equipment design which requires a significant amount of human intervention during a test, leading to attendant human error.
The sensing devices employed to detect movement of the piston past the starting and termination points comprise combination light source and light sensitive elements which detect the presence of the liquid mercury seal. Any misalignment or skewing of the piston relative to the container introduces an error into the flow rate reading. Also, limitations on the flow rate reading result from the limitations on the lack of flexibility of positioning the sensor devices. In addition, the apparatus of the prior art cannot provide a plurality of flow rate readings at closely spaced intervals between the aforesaid starting and termination points, since the prior art apparatus yields a total elapsed time reading as opposed to a true flow rate reading, nor does it provide flow rate readings which are adjusted to standard temperature and pressure. This is due to the fact that there is no technique available for taking into account unexpected changes in measured temperature and/or pressure which do occur during a test interval.